Difference between Delta and Estuary
Estuary and Delta both are formed at the places where rivers meet the sea or drain their water into the sea. Though both are formed by the rivers, they are not similar. Let us see how a delta differs from an estuary!
Delta:
It is a wetland that is formed at the place where a river empties its water into the ocean or where it meets the ocean. It is formed when a river enters into the sea and leaves the deposits of sand, clay and slit around its mouth before entering the sea. The mouth of the river is the place where a river meets a water body like the sea. The deposits build layers to make a platform called alluvium. The river water overflows alluvium and gets divided into a number of branches called distributaries. The distributaries comprise delta which looks like a tree with branches or a triangular fan.
Deltas are fertile areas which have high agricultural productivity so often support large populations. The Ganges Brahmaputra Delta is the largest river delta in the world. A delta can be divided into four parts which are as follows:
- Subaqueous: This part remains below the mark of the low tide and consist s of a fine slit.
- Subaerial: This part is located above the mark of low tide and consists of sand and rocks.
- Upper delta plain: It is the point where the delta starts and contains the largest particles.
- Lower delta plain: It is the point where the river flows into the other water body.
Estuary:
Estuary refers to a partially enclosed water body connected to the open sea and one or more rivers flowing into it. It is formed when a river does not form distributaries before meeting or entering the sea, rather meets the sea in a single line. This lower course of the river is called an estuary. It is generally formed in the areas of high tides and rift valleys. The coastal areas near estuaries can be used as natural harbours. An estuary has many types which are as follows:
- Coastal Plains: In this type of estuaries, valleys are generally shallow with sloping bottoms.
- Tectonic estuary: It is formed when the sea water fills in the hole or basin created by the sinking land.
- Bar built: It is usually shallow with reduced tidal action and is formed when sandbars or barrier islands are built up due to ocean waves and currents.
- Fjords: It has an elongated, U-shaped basin and a barrier that separates it from the sea.
Based on the above information, some of the key differences between Delta and Estuary are as follows:
| Estuary | Delta |
|---|---|
| It is a partially enclosed waterbody with brackish water at the place where a river meets the sea. | It is a wetland formed due to the deposition of sediments by rivers at the mouth of the river where a river divides into distributaries before entering the sea. |
| It is the funnel-shaped mouth of a river where tides move in and out. | It is a triangle shaped land at the river’s mouth travelled across by the distributaries of the river. |
| In India, the rivers Tapti and Narmada rivers form the estuary. | In India, Delta is formed by the Godavari, Krishna, Cauvery, Ganga, Mahanadi, Brahmaputra etc. |
| It is formed when rivers encounter high tides. | It is formed when a river encounters low tides. |
| It is a fertile land with high agricultural productivity. | The land nearby estuary is not fertile. |
| It is suitable for agricultural activities. | It is suitable for fishing activities. |
| Types: coastal plain estuaries, tectonic estuaries, bar-built estuaries and fjord estuaries. | Types: Fan-shaped, cuspate, bird’s foot. |